Bird of the Month: Pacific Wren
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
The big song of the little Pacific Wren is familiar in the old-growth forests of the Pacific Northwest.
Pacific Wren
Scientific Name: Troglodytes pacificus
Length: 4”
Wingspan: 5.5”
Weight: 0.62 oz (9 g)
AOU Alpha Code: PAWR
SUPER SINGER
The long and loud cascade of trills and warbles that seem to fill the forest is amazing considering it comes from one of our smallest birds. The song is a joy in the depth of the forest. Part of the enjoyment rises from the song’s complexity. Pacific Wrens have five different introductions to their song, and each introduction can be followed by a variety of song types. They sing most during the morning, but also sing anytime of the day, expressing hundreds of songs. The song of the Pacific Wren can be heard at The Macaulay Library.
ALTITUDINAL MIGRANT
Pacific Wrens are permanent residents in the west, but they often migrate within their breeding range. Some wrens escape the cold and snow by migrating to lower elevations anytime between late July and November (Bent, 1964a). They depart the wintering grounds in March and begin movement to higher elevation to search for a suitable cavity in which to build their nest.
FOREST FLOOR SPECIALIST
Pacific Wrens are closely associated with complex forest floors in coniferous forests preferring habitat with dead wood such as fallen logs, coarse woody debris, stumps, and root wads. In the Pacific Northwest, breeding of these forest dwellers is broadly correlated with salmon streams. This may be because of the increased abundance of invertebrates which feed on the carcasses of dead salmon and the likelihood of increased nutrients in the soil in these areas (Toews and Irwin).
A natural cavity in a tree or upturned root wads provide good sites for nesting, but old woodpecker nest holes, holes in streambanks, and sometimes hollows in moss are also used by Pacific Wrens. Like some other species of wrens, the males build several nests from which the female chooses one and then both complete the nest using grasses, moss, weeds, animal hair, and feathers. Typically, 5-6 eggs are deposited. Incubation by the female lasts about two weeks. Both parents feed the nestlings, which fledge in another two weeks or so (Kaufman).
Pacific Wren by Andy McCormick
RECENTLY SPLIT FROM WINTER WREN
In 2010 the American Ornithological Union split the Winter Wren into three separate species. The Winter Wren (T. hiemalis) of eastern North America retains the original name, and the Eurasian Wren (T. troglodytes), is simply called Wren in Europe. All three remain in the genus Troglodytes, from Greek for one who creeps into holes, a caveman, in reference to the behavior of poking around in crevices and holes for food or searching for nesting sites (Holloway). The species epithet pacificus denotes its range as a western North American species. (Please see the Note on Taxonomy below.)
STATUS AND DISTRIBUTION
Pacific Wrens are common in their forest habitat and will breed in a range from Alaska south through British Columbia to the eastern slope of the Rocky Mountains including western Alberta, and into parts of Montana. Along the coast they breed in Washington, Oregon, and California as far south as Monterey. The numbers of Pacific Wrens are greater in larger tracts of forest. More nests are found farther from the forest edges and fragmentation of the forest negatively affects their numbers. These wrens winter toward the coast and along the foothills of the western slopes of the Cascades and Sierra Nevada mountains (Toews and Irwin).
Given the Pacific Wren’s recent designation as a separate species, there are no conservation or management programs targeting this species. However, previous research studies of the then Winter Wren in the current range of the Pacific Wren indicate that the bird is much more abundant in old growth and mature forests than in younger even-aged forests. “Retaining continuous, unfragmented areas of unlogged mature and old-growth forests will provide optimal wren habitat” (Toews and Irwin).
A NOTE ON TAXONOMY
As early as 1864 Spencer Fullerton Baird (1823-1887), after whom Baird’s Sparrow and Baird’s Sandpiper are named, identified the Western Winter Wren as a separate species. In his description he noted, “The underparts are more rufous, the tarsi appear shorter, and the claws decidedly larger” (Bent, 1964a). Robert Ridgway (1850-1929), a protégé of Baird’s and for whom Ridgway’s Rail is named, concurred with this assessment (Mearns and Mearns). Ridgway went a step further and recommended that all the Winter Wrens be categorized into their own genus.
However, the Western Winter Wren was lumped under the name Winter Wren for decades. Recent mitochondrial DNA and vocal differences among these wrens led to the recent split in 2010. These wrens are still the subject of taxonomic debate and some ornithologists have resurrected Ridgway’s recommendations to place the three wrens in their own genus (Toews and Irwin). Eleven species and 19 subspecies of wrens in the Western Hemisphere, most of which are in Mexico, and Central and South America, and the Eurasian Wren and its 30 subspecies are all included the genus Troglodytes. There is clearly more research needed to determine the relationships among these wrens.
Photo by Erik Gauger from Getty Images. References available upon request from amccormick@eastsideaudubon.org.